Comments on: Reshape a matrix without using a for loop

By: dhull

dhull — Mon, 16 Nov 2009 20:44:59 +0000

@Niken,

Create the string and then display it at the end. DISP is going to automatically put a line feed carriage return in there.

Doug

By: niken

niken — Mon, 16 Nov 2009 11:15:52 +0000

I have a problem related to loop for string

how to make

y = havehavehave……

i used
n=1;
k=’used’;
while k=<5
disp(k)
n=n+1;
end

the result is
have
have
have
heve

how to make the result is y=havehavehavehave ?

By: dhull

dhull — Tue, 10 Nov 2009 21:04:59 +0000

a  = [11 1; 12 1; 23 2; 24 2]

target = 2;
[vr, vc] = find(a(:,2) == target);

newMatrix = a(vr, :)

By: Carolyn

Carolyn — Tue, 10 Nov 2009 00:30:53 +0000

Hey everyone. I am having a problem that ‘kind of’ relates to this. I have a mtx that is 9511×2, and I am trying to break it up according to the value in the second column, into smaller matrices for each value. for example i have

345 2
367 2
122 2
12 2
345 3
12 3
34 3

i want to end up with a mtx
345 2
367 2
122 2
12 2

and another
345 3
12 3
34 3

etc

so that I can use the each on its own for further manipulation. I’ve tried to used if else statements and such to delete rows, etc. but it is slow, not working, and I keep making loops that run forever (and I’m on a mac so I’m pretty sure I don’t have a break key). I know there has to be an easy way to do this, please help!

By: dhull

dhull — Mon, 02 Nov 2009 16:24:00 +0000

@"Crazee" When I am faced with a problem like this, I make a simple test case and see what happens. Look at this:

a = [1 2; 3 4]
A(:,:,1) = a
A(:,:,2) = a+4
A(:,:,:,2) = A + 10
reshape(A,[2,8])

a =

     1     2
     3     4


A =

     1     2
     3     4


A(:,:,1) =

     1     2
     3     4


A(:,:,2) =

     5     6
     7     8


A(:,:,1,1) =

     1     2
     3     4


A(:,:,2,1) =

     5     6
     7     8


A(:,:,1,2) =

    11    12
    13    14


A(:,:,2,2) =

    15    16
    17    18


ans =

     1     2     5     6    11    12    15    16
     3     4     7     8    13    14    17    18

By: crazee

crazee — Tue, 27 Oct 2009 20:32:16 +0000

Hi Doug,

I have a question. I have a 4-D matrix like 1000×2x2×10. I reshape it to a 2-D 1000×40 matrix using:
newmatrix = reshape(oldmatrix,1000,2*2*10)

I wanted to know how is the reshape working? Basically I wanted to know what are the 40 columns in the new matrix corresponding to the original dimensions (2×2x10) of my old matrix. Does it go like:
newmatrix(:,1) = oldmatrix(:,1,1,1)
newmatrix(:,2) = oldmatrix(:,1,1,2)
.
.
newmatrix(:,11) = oldmatrix(:,1,2,1)
.
.
newmatrix(:,21) = oldmatrix(:,2,1,1)
.
.
newmatrix(:,31) = oldmatrix(:,2,2,1)
.
.
newmatrix(:,40) = oldmatrix(:,2,2,10)

Appreciate your help. Thanks!

By: dhull

dhull — Wed, 14 Oct 2009 13:09:04 +0000

@asad,

M = magic(4)
M(:)’

Doug

By: asad

asad — Wed, 14 Oct 2009 13:02:35 +0000

i am the matlab beginer.i have to convert any n*n matrix into a single row vector.plz help

By: dhull

dhull — Mon, 14 Sep 2009 15:07:06 +0000

@Faisal,

What is a “groups matrix”?

Doug

By: Faisal

Faisal — Sat, 12 Sep 2009 12:42:38 +0000

dear all

i am a beginner in matlab, i have some problem. i have matrix with 500×500 dimension, i want to partition in each have 20×20 dimension so there is have 25 groups matrix. what the code looping in matlab. thx